It's been almost a century since the discovery of cosmic rays -- particles that zip through the universe at close to the speed of light. Yet scientists still don't fully agree on where they come from.
HALZEN: Theorists are sure they know where the cosmic rays come from. Unfortunately, different groups have different answers. [:10]
Francis Halzen is the director of a project called IceCube. It consists of thousands of light detectors buried in the ice at the South Pole. Its goal is to detect particles that can be produced by cosmic rays, known as neutrinos. They travel through the universe unimpeded -- only one in a trillion trillion trillion ever interacts with any other form of matter. But that occasional interaction may be just enough to tell us where they come from.
HALZEN: Cosmic rays come in two flavors. Some are produced in the galaxy and some are produced outside the galaxy. The first one, the standard answer is that cosmic rays are produced in supernova explosions. That has become textbook physics; the only problem is there's no evidence for this. We are still trying to prove this. If we saw a neutrino from the direction of a supernova remnant, the problem would be solved. It's almost more interesting not to see neutrinos from supernova. There are still people who doubt that that's the right solution. [:37]
The cosmic rays from beyond the galaxy are uncertain, too. They may come from the supermassive black holes at the hearts of galaxies, or from the most powerful explosions in the universe -- explosions that create black holes. IceCube will try to resolve that issue, too.
More about IceCube tomorrow.
Script by Damond Benningfield, Copyright 2009